A ninth biker was arrested Monday night in Brooklyn in connection with the Alexian Lien assault.

Jason Brown, 40, is from Brooklyn.

He is charged with gang assault, assault and criminal mischief.

He is expected to be arraigned Tuesday.

Meantime, an undercover police detective arrested in a motorcyclist-SUV melee no longer plans to testify before a grand jury, his lawyer said Monday.

Attorney John Arlia initially indicated that Detective Wojciech Braszczok wanted to speak to the Manhattan grand jury that’s considering indicting him. But Arlia said Monday he’s advised Braszczok not to do so “because the evidence speaks for him.”

“My client has complete confidence and faith this grand jury will determine that he in no way intended to injure, nor act in any way to injure” an SUV driver who was beaten by several other bikers, the attorney said. Video and other evidence will show Braszczok didn’t come close to contact with the driver, Arlia said.

The Manhattan district attorney’s office has said Braszczok nonetheless actively participated in the attack by shattering the SUV’s back window and kicking its passenger side, and he has been charged with gang assault. The DA’s office declined to comment Monday on his decision not to testify.

Many defendants ultimately choose not to testify before grand juries, for various reasons. It’s not uncommon for defendants to give notice that they want to appear and then change their minds.

Braszczok was off-duty when he participated in a Sept. 29 motorcycle rally that took a violent turn. He’s one of several riders who have since been arrested.

After the SUV driver bumped a bike that had slowed in front of it, motorcyclists surrounded and converged on the Range Rover SUV; its driver fled in fear for the loved ones riding with him and ran over a biker, and motorcyclists chased him, pulled him from the vehicle and attacked him, police and prosecutors say. The encounters were partly caught on a helmet-camera video posted online.

The SUV driver, Alexian Lien, hasn’t been charged with any crime.

Braszczok did nothing to stop the assault or summon help, didn’t report having been there to his superiors for a few days, and wasn’t straightforward when he did, prosecutors said.

The detective was stripped of his gun and badge after internal affairs investigators discovered he saw at least part of the confrontation. He initially told authorities and his union that he didn’t intervene in the attack partly because he works undercover.

Arlia has said that the window Braszczok is accused of breaking already had a sizeable hole in it. The detective didn’t know other participants in the rally, which was organized online, and he pursued Lien only to prevent his flight after the SUV ran down and seriously injured motorcyclist Edwin Mieses Jr., Arlia said.

“The facts cannot be changed to lump him into an attack he was not a part of. We owe him and his family at least that much,” Arlia said by phone Monday.

Braszczok (whose name is pronounced VOY’-chek BRAZH’-ahk) has been a police officer for a decade.

It’s unclear when the grand jury might vote on whether to indict him.

A spokesman for Lien didn’t immediately return a call Monday.

(AP)